Inter-tropical evidence for rapid climate change about 4000 years before present: a review
by
Robert Marchant
Institute of Biodiversity and Ecosystem Dynamics, Faculty of Science, University of Amsterdam
Coauthors: Henry Hooghiemstra

About 4000 years before present (yr BP) a relatively rapid climate shift is recorded at numerous sites throughout the equatorial region. The character of this shift is different depending on location. Sites across equatorial Africa record a shift to relatively arid conditions as recorded by decreased hydrological budget of numerous swamps and lakes. Reconstructed vegetation similarly records a transition to more xeric associations and higher incidence of fire than previously recorded. In the neotopics a comparable shift in the mid-Holocene is recorded by a rapid vegetation change. Unlike that in Africa, the neotropical signal is primarily in response to a wetter environment between 4000 and 3000 yr BP. The vegetation response is supported by higher lake levels, e.g. Titicaca and Lake Valencia. At many lowland sites this transition is characterised by a marked increase in the presence of palms (Mauritia and Mauritella) that began approximately 3800 BP, possibly also in response to a shorter dry season and / or human influence.

Although the driving mechanism responsible for this period of relatively rapid climate change is not quantified, it is thought to be related to a combination of decline in monsoon activity, a northward expansion of polar frontal systems combined with greater southward migration of the ITCZ during the southern hemisphere summers and consequent increase in wetter climates in north-western South America. These changes are roughly coincident with decreases in North Atlantic SST and surface salinity. Such decreases in North Atlantic thermohaline circulation may result from a resonance in the system initiated by freshwater inputs from melting of the Laurentide Ice Sheet around 8200 yr BP. Given the widespread occurrence of this signal, this period of change is highly interesting and its characterisation should/will be a target of future targeted investigation.

Date received: March 5, 2002

Copyright © 2002 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caiq-53.